Positive control for the Binax Filariasis Now test

Purpose of the positive control antigen: The Binax Filariasis Now test detects circulating Wuchereria bancrofti antigen in human blood. The test kit has a shelf-life of at least 3 months at ambient temperatures, and it is stable for at least 9 months when it is stored at 5C. Binax conducts extensive quality control testing at their manufacturing facility, and they stand by the quality of the tests when they are shipped. They store the tests in the cold at their facility after they are manufactured, and kits are generally shipped with cold packs. However, breaks in the cold chain can occur during shipping, in customs, and at other times before the tests are used in the field. This positive control filarial antigen can be used in endemic areas to verify that the tests have not lost sensitivity in transit or during storage before they are used in the field.  

Description of the antigen: The positive control filarial antigen was prepared from Dirofilaria immitis adult worm extract as previously described (J Immunol 1985;134:1185 1191). The antigen contains the epitope present in circulating Wuchereria bancrofti antigen that is detected by the Binax Filariasis Now test. Tests in the Weil laboratory have shown that this antigen is stable for years at -20C and that the diluted antigen is stable for at least 4 weeks at 37C, 25C, 4C.

The positive control is provided in screwtop cryotubes (4 ng/ml in PBS with azide preservative, 0.5 ml per tube). The tubes can be shipped at ambient temperatures, but the antigen should be stored at -20C or at 4C.

Procedure: The antigen is used instead of blood in the Binax Filariasis Now test according to the manufacturer’s instructions. Briefly, 100 μl (0.1 ml) of antigen is placed on the sample pad and the card is closed. If the card is working properly, a clear and distinct “T” line should be visible when the card is read at 10 minutes.

If the “T” line fails to appear or if it is faint/difficult to see, this suggests that the card has lost sensitivity and that other cards shipped and stored with the tested card may not be sensitive for detecting filarial antigenemia in human blood.

Contact information: Please contact Kurt Curtis (kcurtis@im.wustl.edu) or Gary Weil (gweil@im.wustl.edu) with questions regarding the use of this antigen.

Notes: The Weil laboratory has donated the positive control filarial antigen to the NIAID Filariasis Research Resources Repository (FR3) to benefit filariasis research and control efforts. It is for research and quality control purposes only, and it should not be sold or used for commercial purposes or for diagnosis of human infections. The antigen is not officially linked to or endorsed by Binax Inc. or their parent company (Inverness Medical Professional Diagnostics, Inverness Medical Innovations).